Crystallization Separation Of AlCl₃·6H₂O From Acid Leaching Liquor Of Coal Fly Ash

Extraction of alumina from coal fly ash is one of the important utilization ways of coal fly ash."Sodium carbonate activation-acid leaching" technology can make the dissolution of alumina in fly ash by acid leaching method reaching 90% or more.In order to solve the problem of high consumption of sodium carbonate,two optimization processesincluding "pre-desilication of fly ash-sodium carbonate activation-acid leaching" and " co-activation of red mud and sodium carbonate-acid leaching" were founded.The addition of sodium carbonate and red mud,however,makes the compositions of the acid leachate are complicated,which result in the separation of the aluminum salt in the acid leaching solution becoming one of the bottlenecks of hindering the industrial application of the process.This paper focuses on the separation method of aluminum salts in Acid Leaching Liquor of fly ash.Two kinds of separation methods including adding concentrated hydrochloric acid and evaporative crystallization.The crystallization temperature,the concentration of hydrochloric acid,the amount of concentrated hydrochloric acid adding and other aspects of the process conditions,the preparation of crystalline aluminum chloride product were explored.Additionally,the phase equilibrium of Acid Leaching Liquor system was discussed and the corresponding phase diagrams were plotted.This work provides theoretical support for the optimization process.The main contents and conclusions are as follows:?1?The process conditions of separatiing crystalline aluminum chloride from the acid leaching liquor of fly ash by adding concentrated hydrochloric acid crystallization were examinedand crystalline aluminum chloride product was prepared using the obtained process conditions.The concentration of acid leachate has a greater impact on the crystallization of aluminum chloride and acid consumption.In order to reduce the consumption of hydrochloric acid and increase the crystallization rate of aluminum chloride,40% of the mother liquor concentrated rate was selected.In addition,the effect of temperature is also very significant.When the temperature increased from 25 ? to 80 ?,the total amount of AlCl₃·6H₂O crystal reduced by about 50%.The higher the temperature,the lower the content of aluminum chloride and the higher the content of sodium chloride in the crystal.So the determined separation conditions were 40% of the concentration,4.5 times of the hydrochloric acid adding to the mother liquor ratio,and 80 ? of the crystallization temperature,when the purity of the isolated aluminum chloride product reached 98.4%.?2?The salting-out regularity at different temperatures of the acid leaching liquor of fly ash was studied.NaCl is precipitated firstly when vaporated at different temperatures.When the precipitation rate of NaCl is about 90%,aluminum chloride began to precipitate quickly.The temperature has a greater effect on the precipitation of the other impurities such as calcium chloride and ferric chloride in the acid leachate system.The precipitation rate of calcium salt and iron salt is larger when the temperature is high.The determined separation conditions were separating sodium chloride at 60? and then separating aluminum chloride when the temperature decreased to room temperature.Under these conditions,sodium chloride with a purity of 99.1% and crystalline aluminum chloride with that of 98.1% were obtained.?3?The solubility of AlCl₃-NaCl-H₂O and AlCl₃-NaCl-H₂O + CH₃CH₂OH at various temperatures and hydrochloric acid concentrations were measured by isothermal dissolution equilibrium method,and plotted the corresponding phase diagrams.The results show that the acid concentration and temperature have a great influence on the phase equilibrium of the system.Ethanol has a great influence on the crystallization of NaCl.The solubility of these two salts is very small under acidic conditions because Cl-in hydrochloric acid has a strong ionic effect with these two salts.In addition,the results of the phase diagram shows that the lower temperature is beneficial to the precipitation of NaCl,which is consistent with the results of the results of process experiment.The process design and optimization through the phase diagram were carried out.In addition,the conclusion of the phase diagram also theoretically verified the results of the experimental process.